“Jumping [over] the broom symbolised various things depending on the culture. In the American south, the custom determined who ran the household. Whoever jumped highest over the broom was the decision maker of the household.
Among southern Africans, who were largely not a part of the Atlantic slave trade, it represented the wife's commitment or willingness to clean the courtyard of the new home she had joined.
In England, jumping over the broom (or sometimes walking over a broom), became nominally synonymous (i.e. "Married over the besom", "living over the brush") with irregular or non-church unions while in America the phrase could be used as a slang expression to describe the act of getting married legally, rather than as one specifying an informal union not recognised by church or state.
Little form of marriage was recognised for enslaved blacks during American slavery. In its absence, the ceremonial jumping of the broom served as an open declaration of settling down in a marriage-like relationship within the slave community. Jumping the broom was always done before witnesses as a public ceremonial announcement to other members of the slave community that a couple chose to become as close to married as was then allowed.
Jumping the broom also fell out of practice due to the stigma it carried, and in some cases still carries, among black Americans wishing to forget the horrors of slavery. Once slavery had ended, many blacks wanted nothing to do with anything associated with that era and discarded the broom jumping practice altogether. The practice did survive in some communities, however, and made a resurgence after the publication of Alex Haley's Roots.
More on Noah's ARC: Jumping the Broom here.